local and regional factors determine community and population structures
DESCRIPTION
Local and regional factors determine community and population structures. Local community structure: result of the interplay of local and regional factors. Local adaptation/population differentiation: enhanced by contrasting local conditions, prevented by ongoing gene flow. - PowerPoint PPT PresentationTRANSCRIPT
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Local and regional factors determine community and population structures
• Local community structure: result of the interplay of local and regional factors.
• Local adaptation/population differentiation: enhanced by contrasting local conditions, prevented by ongoing gene flow.
• Model system: Nature reserve “De Maten”, Genk, with its system of overflows and identical abiotic but contrasting biotic background.
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The development of a model system for study of local adaptation: Scenedesmus
Predator-induced defenceIn Scenedesmus-species• colony formation•Genetic variation present
Hypothesis: Scenedesmus genotypes from a clear pond with high grazing pressure will be bigger and show a
Stronger response to infochemicals
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Isolation of Scenedesmus communities from ecologically contrasting ponds
Pond 15: clear pond withLarge Daphnia, 52 strains Pond 18: turbid pond with small
Zooplankton, 75 strains
Nature reserve“De Maten”, Genk, Belgium
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Problems associated with species identification
• Description of each morphotype as distinct taxon: monograph by Hegewald & Silva lists over 1300 taxa
• Phenotypic plasticity: each genotype produces a variety of morphotypes
• Recent changes using molecular methods, 18S and ITS-region.
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Molecular methods for species delineation
• 18S-rDNA RFLP
• DGGE of the ITS-2 region
• Sequence analysis of ITS-2
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3´-GCGTCGGTTT TTCGACCTGAGC-5´
rDNA ITS2 gene
~ 227 - 264 bp
SSU (18S) large SSUITS 1 ITS 25.8S rDNAsmall (25-28S)
Location of the ITS spacer region on the genome
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10
>AJ249506>AJ237956
>AJ400496>AJ400498
>S4>S112
>AJ400493>AJ400494
>S45>S97
>AJ400499>S93>AJ400505>S104>S108>S122>S24>S27>S29>S59>S5>S62>S63>S65>S81>S94>AJ400502>S70
>S100>S101>S105>S107>S118>S16>S20>S22>S23
>S30>S36
>S42>S46>S51>S58>S60>S72>S74>S85>S86>S87>S90
>S68>S69>S96>S99>S50>S18
>S106>S11>S7>S83
>S38>S49
>S71>S9
>AJ400506>S113
>S28>AJ237959>AJ400504>S12>S114>S35>S52>S8>S98
>AJ237960>AJ237961
>AJ400495>AJ400500
>S39>S41
>AJ400503>S110>S129>S19>S33>S40>S61>S66>S6>S82>S84>S92>S95
>S64>S102>S26>S89>S25
>S44>AJ400497
>S135>S21>S37>S75
>AJ400501>AJ400492
>S34>AJ316581
>S67>AJ237958
>S10>AJ237957
>S43>S13
>S111>S47>S88
“D.communis-clade”
“D.armatus-clade”
“D.opoliensis-clade”
“D.bicellularis?-clade”
“D.brasiliensis-clade”
“Desmodesmus sp.”
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Desmodesmus opoliensis
Desmodesmus armatus
Typical shape, bristles, difference between ponds
Very variable, present in both ponds
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Desmodesmus communis
Present in both ponds, outer cell wall layer
Desmodesmus brasiliensis
Distinctive ribs, short spines
Desmodesmus bicellularis?
Very small, no spines, Morphologically heterogenous, only in turbid pond
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Conclusions
• Agreement of morphological and molecular methods.
• Shifts in species composition though the most
abundant species are present in both ponds.
• Further work at the intraspecific level in progress